We're still piecing together a picture of the shooter, his home life, and the relationship he had with his mother. Can you predict such violent actions? Are there telltale signs? Following a weekend of immeasurable grief, so many questions remain. Why did this happen? Could it have been prevented? I'm so sorry. Reporter: At the center of the mystery, adam lanza's mother, nancy. She struggled with a son with increasing motion nal issues. She said, it's getting harder. He's getting orlando. Reporter: Abc news learned mother and son spent t at a local gun range. Friends say nancy was a single mother doing the best she could. Have she constantly tried to help him and get help for him. She did what she could as a mother. Reporter: On saturday, the family's father released this. Our hearts on go out to all hurt and insxwrurpd we, too, are asking why. He joins a number of other parents who have apologized for a child's violent act. People like tammy roberts, ro who raised jake roberts. He just went on a shooting spree last week. Never could I imagine him being part of such a thing like this. As his mother, he will always be in my heart. Reporter: A similar message that these friends of nancy say she would have given. Could these tragedies have been sprent snd a question that the family, victims, and the nation alike are wondering today. And let's bring in psychiatrist dr. Janet taylor and our legal analyst, dan abrams. Nancy told friends that she thought her son suffered from asperger's. How do you preconvict someone committing a violent act? There are factors that have been linked to violence. Asperger's doesn't necessarily mean that. If there's underlying depression, mood disorder, or paranoia. Those are significant aspects as well. If there's been a transition, a loss of a girlfriend, something like that. He reportedly suffered from a condition where he did not feel any physical pain. Is that an ind carrot of anything? It really is not. The question is, how would a mother have known? There's no way she could have known. There's no way as professionals we can predict who will be violent and commit a mass murder? 1 in every 10 families have adolescents or teens that have emotional disturbances, at home, in the community, at school. We need to address the individuals, get them into timely treatment. There are a lot of questions about why nancy lanza has five weapons in the home, took her son to a gun range where he undoubtedly learned to use them. that she took of school. If the guns are legal, you would hope they would go to a range to learn to use a weapon. Let's remember, she's dead now. She's been shot and killed. She, too, is a victim. There's not going to be legal liability to her. Very naufb these kinds of cases, we see kids shooting other kids. We say, how much responsibility can the parents have? Here, an adult. 20 years old. Not a child. The mother is dead. There are not going to be a ton of leg questions here. Certainly not criminal. It will be tough to think about civil. I think we have to be careful. A number of parents home school their kids successfully. If you have a child with a mental illness, they should not be around guns or fire arms at all. Period.

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